Large scale, long term controlled trials will be conducted by the Prevention and Cancer Control Science Programs during the next decade. Research in controlled trials methodology is being planned which will investigate three aspects of data management associated with these studies. (1) Field test of micro-computer technology for data capture at local clinical sites using formated screen data entry via a keyboard or via handwriting. Systems will be evaluated in terms of equipment, development and maintenance costs, portability, ease of use by data managers and clinicians, and quality of data (including timeliness). (2) Development of micro-processor software for onsite data editing and verification, and onsite assistance in conducting the trial according to protocol specifications, to improve data quality and protocol adherence. (3) Utilization of technological developments in computer networking (machine to machine interface within a clinical center and across geographically diverse centers). Research is also planned which addresses design and sample size estimation of prevention trials, e.g., controlled trials with chemoprevention agents or dietary interventions. Feasibility of such trials depends, in part, on the number of individuals required with respect to the number available, which is a function of the incidence of the targeted cancer in a given population. Since traditional designs for single cancer site mortality reduction range from 5,000 to 20,000 to more than 120,000 subjects, alternative designs are under exploration to enable conduct of these critically needed studies undertaken in a scientifically sound manner within feasible operational and fiscal constraints. Such research has direct relevance to chemoprevention controlled trials, nutrition and cancer studies, the Clinical Community Oncology Program, cancer centers, occupational studies and Phase IV demonstration projects.